更新生产部署配置，调整工作流以支持 prod 分支，移除不再使用的数据库网络变量，并优化文档说明

compose.production.yaml

@@ -32,9 +32,7 @@ x-backend: &backend
     AI_OUTPUT_TOKENS: ${AI_OUTPUT_TOKENS:-4096}
     AI_TIMEOUT: ${AI_TIMEOUT:-180}
     WQ_BASE_URL: ${WQ_BASE_URL:-https://api.worldquantbrain.com}
-  networks:
-    - default
-    - database
+  # Reach the remote PostgreSQL endpoint through the default network's egress.
 
 services:
   backend:
@@ -89,10 +87,6 @@ services:
       start_period: 10s
     restart: unless-stopped
 
-networks:
-  database:
-    external: true
-    name: ${DATABASE_NETWORK:?Set the existing PostgreSQL Docker network}
 volumes:
   caddy_data:
   caddy_config: